No justification for denying obese patients knee replacements

July 24, 2008

There is no justification for denying obese patients knee replacement surgery: They benefit almost as much as anyone else from the procedure, concludes a small study published ahead of print in the Annals of the Rheumatic Diseases.

Around 55,000 knee replacements are performed every year in England to relieve the pain and disability of knee osteoarthritis.

But in some parts of the country the surgery is offered only to patients who are not clinically obese (body mass index (BMI) below 30 kg/m2), on the grounds that obesity is itself a risk factor for knee osteoarthritis.

The research team monitored the progress of 325 people over the age of 45 for around six years after they had had knee replacement surgery.

Their progress was compared with that of 363 general practice patients, matched for age and sex, who had not had knee replacements.

At the start and end of the study, all participants completed a validated questionnaire designed to assess their mobility, mental health and wellbeing (vitality).

To begin with, the patients said they had significantly worse mobility than those in the comparison group, scoring an average of 20 compared with 89.

By the end of the study, mobility in the patients had increased by an average of 6 points, while that in the comparison group had fallen by 14.

Mental health scores, which were similar at the outset, improved in both groups, but while wellbeing fell among both groups, the fall was greater among the patients who had had surgery.

When the researchers restricted their analysis to participants who were obese, the improvements persisted, and BMI did not appear to be a significant factor in this.

But there was a stark contrast in mobility among those who had and had not had the surgery.

Mobility score rose three points among those who had had surgery, but fell 36 points among those who had not had a knee replacement. And among those over the age of 75 who had not had the surgery, mobility score fell 40 points.

"The long term improvement in physical function that we observed in patients who have undergone TKA [knee replacement surgery] is striking when set against the decline that occurred in [the comparison group]," say the authors.

"These benefits extend to patients [who are obese] and, provided appropriate selection criteria are applied with regard to fitness for surgery, there seems no justification for withholding [knee replacement surgery] from patients who are obese," they conclude.

Source: British Medical Journal